Tanning of hides and skins.



ATENT on ERNEST WYNDHAM MERRY, 0F SHEFFIELD, ENGLAND, ASSIGNOR TOINTERNATIONAL IPYROTAN COMPANY, LIMITED, OF LONDON, ENGLAND.

TANNING 0F I-IIDES AND SKINS.-

Be it known that I, ERNEST WYNDIIIAM MERRY, subject of the King of GreatBritain and Ireland, residing at 45 Cherry street,

Bramall Lane, Sheflield, in the county of York, England, have inventednew and useful Improvements in the Tanning of 'Hides and Skins, of whichthe following is a specification.

This invention relates to the tanning of hides and skins by the actionof the known mineral agents, alum and pyrophosphate of sodium and hasfor its object the carrying out of the tanning operation with hides orskins of any character or thickness with thoroughness and certainty in asimple and controllable manner.

I am aware that a process has been described in the specification of theUnited States Patent No. 1,039,150 in which the agents above referred tohave been included in the ingredients of a tanning solution or solutionsof definite strength which it is therein stated may be varied to suitthe different classes and weights of hides being treated and specificproportions of the several ingredients are given as being effective forcow hides of a medium weight. I have discovered that the said process,however,

is only applicable to cow hides and other similar hides of a loosecharacter and small thickness and that when thick hides or hides of afirm character such as ox hides are under treatment it is impossible toproduce a satisfactory tannage even by increasing the strength of thetanning solution by 50%.

As the result of numerous experiments I believe that the permanenttanning action of a solution containing alumand sodium pyrophosphate isdue to the interaction in the pores of the hide of the alum-andthesodium pyrophosphate, whereby there results pyrophosphate of aluminium,which latter is insoluble in water and becomes fixed in the pores of thehide.

My present invention consists in the provision of a tanning solution orsolutions of I such composition and concentration as are hereinafter setforth and within the limits defined. By observing these limits the tan-Specification of Letters Patent.

Patented July 18, 1916.

- Application filed January 12, 1916. Serial No. 71,652.

ning operation can be effected on any class I or thickness of hide witha celerity, certalnty and efliciency which is not at present attalnableby known means.

In describing how my present invention is carried into effect I shalldefine the proportlons employed as a percentage of the welght of hide tobe treated. Sodium pyrophosphate as it is found in commerce contains avarying quantity of the pure anhydrous salt, say, from 45 to per cent.thereof, therefore in the percentages hereinafter given it must beunderstood that the same are based on the pure anhydrous salt Na P OAccording to my present invention; the alum (I refer to the crystallizedsalt with 24 molecules of water of crystallization) must exceed 5 andshould not exceed 7 times the weight of sodium pyrophosphate, forexample 10% of the former and 1.66% of the latter'and the Water must bebetween 20% and 40% of the weight of hide treated, for example 27%.While this latter concentration gives the greater penetrating effect anymuch higher concentration than this is not desirable owing to the riskof graining taking place due to the solution being too small in volumetopermit of the uniformity of strength being maintained throughout thewhole of the volume of solution, particullarily that portion between thelayers of The composition'of the tanning bath is as follows: 10% ammoniaalum, (NH ),SO,,Al (SO 24H O; 1.66% pyrophosphate of soda, Na P O 27%water, and say 5% of washed in the drum with warm water at 8090 F. Thehides are then subjected to the action of a tanning bath containingalum, common salt or some similar substance to counteract the drawingeffect of the alum, and sodium pyrophosphate in water at an initialtemperature of 80"90 F. until the hide is completely penetrated. Thisbath is preferably prepared by dissolving the alum and common salt orits substitute in the desired quantity of hot water and dissolving thesodium pyrophosphate in a separate quantity of hot water and mixing thetwo solutions together. An alternative method which produces the sameresult is to thoroughly mix the substances mentioned in the dry stateand dissolve this mixture in the requisite amount of hot Water. Thetanning bath however prepared is then placed in the drum with the hidesand drummed for 45 minutes or the tanning bath may be added by degreesto the drum if so desired. The mixture after drumming is then run offinto another vessel and the hides transferred to such vessel and placedin the mixture therein or what is usually more convenient the hides andmixture are left in the drum, care being taken that no creasing ormarking occurs. The tannage is allowed to progress for 34 hours orlonger until the hides are tanned through. Alternate drumming andresting may be used to accelerate the process if close heavy hides arebeing treated. The tanned hides are then horsed up for 12 hours (usuallyovernight). The liquor in the drum is then mixed with the coloring bathwhich may be added direct to the drum. The coloring bath is obtained bydissolving each of the desired materials usually gambier and quebracho,in separate quantities of hot Water and finally mixing the solutionsobtained in the usual manner. 3% gambier and'2% quebracho dissolved inas small a quantity of Water as possible will be found suitable butthese quantities may be varied. The hides are rapidly replaced anddrummed for 3 hours. A rather safer method is to drum the hides in theexhausted tanning bath liquor and then gradually add the preparedcoloring bath during that process through the axle of the drum in Wellknown manner.

For certain classes of leather such as sole leather and for close heavyhides it is sometimes found advisable to supplement the tanning processby the following treatment :Taking the hides out of the tanning bath andgiving them a supplementary bath Which is added in two stages prior tothe coloring bath. The first stage consists in the addition of asupplementary bath to the exhausted tanning bath liquor contained in thedrum. The hides are then inserted and drummed for 45 minutes. Thesupplementary bath is prepared in a similar manner to the tanning bathdescribed above. Its composition is :5% ammonia alum, 1.66%pyrophosphate of soda, 27% water, and say 5% common salt or itssubstitute.

The second stage consists in the further addition to the mixture in thedrum of a solution of alum dissolved in as little hot water as possible;the quantity of alum being the same as that used in the supplementarybath. Drumming is now continued for a further 2 hours and the whole thenallowed to stand 12-14 hours after adjusting the hides in the drum toprevent creasing. The hides are then colored by the addition of thecoloring bath to the mixture in the drum using the same method asalready described. The resulting colored hides whether prepared by thesingle or double bath process are finally horsed up for 12-14 hours andthen rinsed through a bath which may con sist of water alone or a 5%solution of borax. After draining, the hides are then finished by one ofthe well known processes in the usual way.

I would have it clearly understood that any soluble aluminium salt maybe substituted for the ammonia alum herein referred to such for exampleas soda alum Na S0,,Al (SO 24H O, potash alum K,SO,,A1 (809 2411 0, oraluminium sulfate .AI,,(SO 18H O.

In using these salts the relative proportions in the formulae given,must be modified so as to maintain the aluminium constituent at itsproper value.

I claim 1. In a process of tanning by-means of alum and sodiumpyrophosphate the treatment of the hides in a tanning solution in whichthe proportion of alum in terms of the crystallized salt with 24molecules of water of crystallization to sodium pyrophosphate in termsof the pure anhydrous salt is in the ratio exceeding 5 up to 7 parts ofalum to 1 part of sodium pyrophosphate.

2. In a process of tanning by means of alum and sodium pyrophosphatethetreatment of the hides in a tanning solution in which the proportion ofalum in terms of the crystallized salt with 24: molecules of water ofcrystallization to sodium pyrophosphate in terms of the pure anhydroussalt is in the ratio exceeding 5 up to 7 parts of alum to 1 part ofsodium pyrophosphate the proportion of the said alum being substantiallyth of the weight of hide treated.

3. In a process of tanning by means of alum and sodium pyrophosphate thetreatment of the hides in a tanning solution in which the proportion ofalum in terms of the crystallized salt with 24 molecules of water 27%,alum 10%, sodium pyrophosphate in terms of the pure anhydrous salt is inthe ratio exceeding 5 up to 7 parts of alum to 1 part of sodiumpyrophosphate the restriction of the quantity of the water in Intestimony whereof I have signed my the tanning bath to from 20% to 40%of the name to this specification in the presence of 10 weight of hidetrealted. f h f 11 two subscribing witnesses.

4. tanning so ution o .t e 0 owing 5 proportions on the weight of hidetreated, ERNEST WYNDHAM MERRY water 27%, alum 10%, sodium pyrophos-Witnesses: phate 1.66% and, say, 5% of a pore opening Doms H. Hrroncocx,agent such as common salt. CHARLES J R. BULLOUGH.

